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Acceptable level of TDS for Ro/DI water?

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  • Acceptable level of TDS for Ro/DI water?

    Hi all,
    Finally getting ready to think about filling the new 220g tank. Just received our TDS meter yesterday. The TDS on our RO/DI water measured 14ppm. Is this going to be a problem, if we use this to set up our tank? What is the acceptable range you would like to see for use in reef tanks?

    Thanks in advance for all your help.

  • #2
    If your DI is working well it should be at, or close to, zero.

    what is the TDS of your RO water before filtering it with the DI?
    400 gallon reef, Bubble King 300, I~Spin, 2 x 10,000K BLV 400W, 2 x 20,000K Radium 400W, 2 x 6,400K Osram 400W, Schuran Jetstream 1, AquaController Pro


    • #3
      Maybe buy a small bottle of distilled water to check the meter?

      “People are very open-minded about new things - as long as they're exactly like the old ones.”
      ...Charles F. Kettering


      • #4
        Reverse Osmosis units can only remove a certain percentage of the solutes of the incoming water. For example on my RO I have around 60 tds coming in and I have 0-1 tds coming out. If you have 500 or more coming in but only 14 coming out then I would consider that pretty good. I would say 10-20tds coming out about the maximum range of of solutes I want coing out of my RO while treating water with normal tds. If you have really hard water and you have 50tds coming out then its not really a big deal for reef tanks because we dont mind extra hardness in our water. If you are concerned about what the last little 14 tds might be composed of, the best thing to do is to request a listing of the tds in your tap from the water treatment plant, maybe DHEC has it also and then you will be able to estimate what solutes are actually getting through.
        Jake Adams
        Reef Builders


        • #5
          If this is your first fill to start the tank I wouldnt worry about it. The DI resin wont remove solutes but it instead exchanges them for relatively unreactive ions.
          Jake Adams
          Reef Builders


          • #6
            The RO membrane is either 98 or 95% depending on the model. ie TDS 500 in the with optimal conditions 10-25 TDS on the out side. The DI should take care of the rest...

            I use an inline dual TDS meter so I can track both my RO unit and my DI separately.
            10x3x2 FOWLR (for now)
            RD12 return, 2 RD12 closed loop, wavebox with extension
            MRC kalkmixer


            • #7

              Our water before going through the RO/DI unit is 147 ppm and coming out at 14 ppm. Biggest concern we have is not wanting this to effect our tank setup/SPS keeping/ZEOmethod. The cartridges were changed a few months ago (no more then a couple hundred gallons ago), not sure if we have a 95 or 98 percent removal membrane. Would like more opinions on if this is 'acceptable' or if we should consider a different RO/DI unit.

              What model RO/DI units does everyone else on here have and where did you get it from???



              • #8
                Hi All -

                Another update, just checked our meter with some DI water and it checked out at 0.00.

                So I guess we are looking more into the option of a new RO/DI...what does everyone recommend? Do not need a huge GPD rating....50 or 70 would do it.

                Would it be a bad thing to do the initial filling with the water from this RO/DI...that way we can start filling before waiting for the new unit to arrive?

                Opinions/Suggestions appreciated.


                • #9
                  Well yet another update.

                  Went and got 2 new DI cartridges, swapped out the RO cartridges few months ago, put in the new DI filters and we are now at 3-4 ppm so I have a feeling this is fine. Still would like to know what RO/DI units you guys are recommending though.



                  • #10
                    You could always add another DI filter. This is where I get my replacement cartridges Also ask him how to test a TDS meter to see if it calibrated right. There is a simple test using certain brand of bottled water. For myself I am no longer going to rely on a TDS and just change my cartridges on a timed schedule. I'm going to start changing my DI cartridge 3-4x's yr.,prefilter/carbon 2x's yr and my RO membrane 1x yr. IMO having a problem due to makeup water can be far more expensive than replacing filters. Again JMO
                    Take Care,